Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$42.60	11.439%	$47.473	$47.47	$47.45	$47.50
Purchase #2	$160.82	5.598%	$169.8227	$169.82	$169.80	$169.80
Purchase #3	$104.76	13.740%	$119.154	$119.15	$119.15	$119.20
Purchase #4	$223.84	13.466%	$253.9823	$253.98	$254.00	$254.00
Purchase #5	$88.91	12.736%	$100.2336	$100.23	$100.25	$100.20
Purchase #6	$109.94	7.405%	$118.0811	$118.08	$118.10	$118.10
Purchase #7	$115.29	4.172%	$120.0999	$120.10	$120.10	$120.10
7 purchase totals =	$846.16		$928.8466	$928.83	$928.85	$928.90